Wedge shape safety stop

ABSTRACT

A safety stop is provided for stopping a movable member having at least one set of opposed wheels for gripping a rail. The stop has a track on each of opposite sides forming a wedge shape of a narrow end progressively widening to a wide end in a direction of travel of the movable member. With the opposed wheels of the movable member respectively at opposite sides of the wedge shape member, the tracks of the wedge shape member engage and impart a spreading strain to the opposed wheels as the movable member moves in the direction of travel. The opposed wheels of the movable member comprise a deformable material to absorb the kinetic energy of the movable member. The tracks of the stop additionally may have undulating features comprising concave and convex surfaces in the direction of motion.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of copending U.S. patentapplication Ser. No. 12/895,570, filed Sep. 30, 2010.

FIELD OF THE INVENTION

This invention relates to end stops, and more particularly to safetystops for stopping a movable member.

BACKGROUND OF THE INVENTION

An ever present desire is to achieve faster speeds for movable members,one example comprising robots of data storage libraries. Hence, themovable members tend to be made lighter and possibly likely to sustaindamage if reaching an end of travel at full speed. In the case ofrobots, the modern robots may be made of more light weight plastic partsor with other light weight materials. While these light weight fastmoving robots are ideal for performance of moving quickly within alibrary system, there exists a possibility of a code bug or hardwareerror that could make the robot run out of control at full speed intothe end of its travel of its rails. A need therefore exists to stop anout of control movable member without destroying the operating mechanismof the light weight member.

SUMMARY OF THE INVENTION

Methods are provided for stopping a movable member, such as a movablerobot.

In one embodiment, a safety stop is provided for stopping a movablemember having at least one set of opposed wheels configured to engageopposite sides of at least one rail. The stop member has a track on eachof opposite sides forming a wedge shape of a narrow end progressivelywidening to a wide end in a direction of travel of the movable memberwith respect to the stop member. With the opposed wheels of the movablemember respectively at opposite sides of the wedge shape member, thetracks of the wedge shape member are configured to engage and impart aspreading strain to the opposed wheels as the movable member moves inthe direction of travel.

For a fuller understanding of the present invention, reference should bemade to the following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a movable member with opposed wheels whichmay implement aspects of the present invention;

FIG. 2 is an illustration of the movable member of FIG. 1 with theopposed wheels on opposing sides of a guide rail;

FIG. 3 is an illustration of the movable member and guide rail of FIG. 2with a safety stop in accordance with the present invention;

FIGS. 4 and 5 are illustrations of the safety stop of FIG. 3; and

FIG. 6 is a flow chart depicting an exemplary method of the operation ofthe safety stop and movable member of FIGS. 3, 4 and 5.

DETAILED DESCRIPTION OF THE INVENTION

This invention is described in preferred embodiments in the followingdescription with reference to the Figures, in which like numbersrepresent the same or similar elements. While this invention isdescribed in terms of the best mode for achieving this invention'sobjectives, it will be appreciated by those skilled in the art thatvariations may be accomplished in view of these teachings withoutdeviating from the spirit or scope of the invention.

Referring to FIGS. 1 and 2, an example of a movable member 100 isillustrated, which in the example, comprises a robot mechanism usable ina data storage library system. The movable member comprises opposedguide wheels 105 mounted on guide wheel brackets 110 so as to bepositioned on opposing sides of guide rail 112.

A drive motor 115 of the movable member drives a pinion 117 to mesh withrack 118 to drive the movable member 100 along the guide rail 112. Inone example, the robot mechanism comprising the movable member isarranged to transport a tape cartridge 120.

In one embodiment, 4 sets of opposed wheels 105 are provided for themovable member, in the example, at each side of the movable member.Additionally, one set 130 of opposed wheels 105 is located towards oneend of the moveable member 100, and another set 135 is located displacedfrom the other set of opposed wheels in the direction of motion of themoveable member. Both sets 130 and 135 are at the same side of themovable member and are configured to engage opposite sides of the rail112. In the example, 2 similar sets of opposed wheels are provided atthe other side of the movable member, set 140 and set 145 are locateddisplaced from each other in the direction of motion of the moveablemember.

In the example of a robot mechanism as the movable member 100, guiderollers 148 position the movable member laterally with respect to therail 112.

Referring additionally to FIGS. 3, 4 and 5, a wedge shape safety stop150 is provided at the end of rail 112 and has a slot 152 configured toposition the safety stop on the rail.

The safety stop comprises a wedge shape stop member 150 that has tracks160, 162 on each of opposite sides forming a wedge shape of a narrow endprogressively widening to a wide end in a direction of travel of themovable member 100 with respect to the stop member 150. With the opposedwheels of the movable member respectively at opposite sides of the wedgeshape member, the tracks of the wedge shape member are configured toengage and impart a spreading strain to the opposed wheels 105 as themovable member moves in the direction of travel.

The leading end of the stop member 150 at each side of slot 152 at eachtrack 160, 162 comprises a leading edge rounded ramp 165, 167 extendingforward of the track in a direction opposite the direction of motion toa point adjacent the central slot 152. The rounded ramp is configured toguide an opposed wheel onto the track.

Guide walls 170 are provided at each side of each track. The guide wallsguide the opposed wheels on each track 160, 162, to retain the opposedwheels on each track.

The opposed wheels 105 of the movable member comprise at least partiallya deformable material. In the illustrated example, the opposed wheels,see wheels 130, each comprises a bearing 180 with a thick outer wheel ofrubber, polyurethane, high density foam, or other deformable material182.

The deformation of each of the opposed wheels absorbs the kinetic energyof the movable member.

The walls 170 of safety stop 150, in one embodiment, may be narrowedtowards the spaced apart end of the tracks 160, 162 so as to engage thebulging sides of deformable opposed wheels and impart a frictional forceto the wheels, absorbing additional kinetic energy.

The wheels are mounted to posts on a bracket 110 that, for example, isplastic, and that has some flexibility to allow the guide wheels tospread apart when engaging the wedge shape stop member 150.

The wedge shape of the stop member tracks 160, 162, progressivelyincreases the separation distance between the opposed wheels 105 asshown by arrows 190, and engages and imparts a spreading strain to theopposed wheels 105 as the movable member moves in the direction oftravel. The spreading strain deforms the deformable portion 182 of theopposed wheels, absorbing the kinetic energy of the moveable member 100,causing it to slow down and come to a stop. Further, the mount 110 forthe opposing wheels allows the opposed wheels to be forced by thespreading strain to be spread apart, and absorbs additional kineticenergy.

Still further, in one embodiment, the movable member 100 comprises atleast two sets of the opposed wheels 105, for example, the sets 130 and135 displaced from each other in the direction of travel. Thus, whileone set of wheels 130 is engaged by the tracks of the wedge shape stopmember, the engagement of the second set of wheels 135 increases theabsorption of kinetic energy.

In addition, the wedge shape stop member comprises bump features 200therealong. In one embodiment, the bump features 200 comprise concavesurfaces in the direction of motion, the concave surfaces having radiigreater than that of the opposed wheels. The bump features cause theopposed wheels to move up and down more frequently when moving acrossthe wedge shape of the tracks to absorb even more energy, and increasethe resisting force in the direction of the motion of the movable memberto assist in bringing the movable member to a safe stop.

Another feature is a hard stop 205 at the wide end of the tracks of thewedge shape member. The hard stop prevents the movable member fromfalling off the end of the safety stop.

As one alternative, the opposed wheels may be solid, and the tracks 160,162 of the stop member comprise deformable material of rubber,polyurethane, high density foam, or other deformable material.

As another alternative, or in addition, the tracks 160, 162 may becoated with a tacky material to absorb kinetic energy.

Referring additionally to FIG. 6, step 220 comprises providing the wedgeshape stop 150. The stop member has a track 160, 162 on each of oppositesides forming a wedge shape of a narrow end progressively widening to awide end in a direction of travel of the movable member with respect tothe stop member as shown by arrows 190. Guide walls 170 are provided ateach side of each track and the tracks may comprise bump features 200 asdiscussed above.

In step 225, if the movable member is operating normally, it may operatesome distance from the stop 150, and if it goes to the end, it candetect the stop 150 by bumping into the rounded leading edges 165, 167of the stop. If the mechanism instead is in a runaway condition, asillustrated by step 225, in step 230, the opposed wheels are engaged atthe tracks 160, 162 on each of opposite sides of the stop member, as thewheels are driven over the leading edges 165, 167.

In step 235, the guide walls 170 trap the opposed wheels and guide themonto the tracks 160, 162 so as to not slip off the tracks. In step 240,as the movable member moves up the wedge shape of the tracks, theimparted strain of the wedge shape causes the deformable portion of theopposed wheels 130 to deform, and the posts holding the wheels may beginto spread apart as the bracket 110 also deforms. These actions absorbthe kinetic energy of the movable member. Additionally, the bumpfeatures 200 comprise concave surfaces in the direction of motion, theconcave surfaces having radii greater than that of the opposed wheels.The bump features cause the opposed wheels 130 to move up and down morefrequently when moving across the wedge shape of the tracks to absorbeven more energy, and increase the resisting force in the direction ofthe motion of the movable member to assist in bringing the movablemember 100 to a safe stop. Alternatively, the bump features 200 may havesmaller radii, or be convex, or be of any shape that is arranged todeflect the opposed wheels 130 to absorb energy.

The subsequent movements of a second set of wheels 135, whose deformableportions also deform, increase the absorption of kinetic energy.

Additionally, any tacky coating of the tracks 160, 162 absorbs kineticenergy as the opposed wheels move along the track.

Still further, any narrowing of the walls 170 squeezes the sides of theopposed wheels and imparts a frictional force to the wheels, absorbingadditional energy.

In alternative or additional embodiments, in step 240, as the movablemember moves up the wedge shape of the tracks, the imparted strain ofthe wedge shape causes the tracks 160, 162 to deform as the opposedwheels move into the tracks, thereby absorbing kinetic energy of themovable member.

If the kinetic energy is too great to have the stop 150 completely stopthe motion of the movable member 100, in step 250, the hard stop 205 atthe wide end of the tracks of the wedge shape member prevents themovable member from falling off the end of the safety stop.

In alternative embodiments, the bracket 110 may be solid and not deform,and the rail 112 may comprise spaced apart rails, each supporting anopposed wheel.

In further alternative embodiments, the wedge shape may extend only ashort distance and the tracks 160, 162 may be parallel thereafter andcomprise bump features 200.

Those of skill in the art will understand that changes may be made withrespect to the methods discussed above, including changes to theordering of the steps. Further, those of skill in the art willunderstand that differing specific component arrangements may beemployed than those illustrated herein.

While the preferred embodiments of the present invention have beenillustrated in detail, it should be apparent that modifications andadaptations to those embodiments may occur to one skilled in the artwithout departing from the scope of the present invention as set forthin the following claims.

What is claimed is:
 1. A method for stopping a movable member, saidmovable member having at least one set of opposed wheels comprising atleast partially a deformable material with circumferential surfacesconfigured to engage opposite sides of at least one rail, comprising thesteps of: engaging, with a stop member having a track on each ofopposite sides forming a wedge shape of a narrow end progressivelywidening to a wide end in a direction of travel of said movable memberwith respect to said stop member, said circumferential surfaces of saidopposed wheels of said movable member at said tracks respectively atopposite sides of said wedge shape member; and imparting, by said tracksof said wedge shape member, a spreading strain to said opposed wheels ofsaid movable member as said movable member moves in said direction oftravel such that deformation of each of said opposed wheels absorbskinetic energy of said movable member.
 2. The method of claim 1, whereinsaid step of imparting a spreading strain comprises: said tracks of saidwedge shape member imparting a varying spreading strain employing bumpfeatures of said tracks, wherein said bump features comprise concavesurfaces in said direction of motion, said concave surfaces having radiigreater than that of said opposed wheels.
 3. The method of claim 1,wherein said step of said stop member engaging said opposed wheels ofsaid movable member comprises guiding said opposed wheels on each saidtrack with guide walls at each side of each said track, said wallsnarrowed towards the spaced apart end of said tracks so as to engage thebulging sides of deformable opposed wheels and impart a frictional forceto said wheels, absorbing additional kinetic energy.